This invention relates to the control of subsidence following underground gasification of coal. Underground gasification of coal results in the formation of a cavity where the coal is removed and subsidence or caving of the overburden into the cavity occurs. In some coal gasification facilities, subsidence has occurred all the way to the surface.
Landowners are entitled by law to subjacent support and lateral support. The former is a support which the underlying land gives to the vertically overlying land and lateral support is that which exists on vertical planes dividing the supporting and supported land. Thus, considerable liability can occur as underground mining takes place. Even if there is no subsidence to the surface, other problems exist. Subsidence can result in environmental problems such as aquifer contamination and operational problems including premature loss of wells.
In the more conventional mining of solid fuels such as coal and oil shale, the room and pillar system has been used. This leaves support pillars in place as rooms of the solid fuel are excavated. Suggestions have been made for recovery of the pillars, one example being shown in Sweeney U.S. Pat. No. 4,440,449, (1984) wherein artificial support members are provided between pillars and the pillars thereafter mined.
In underground coal gasification, it is difficult to control the gasification with air or oxygen injection so that pillars of unaffected coal remain to support the overburden.
An object of this invention is to provide a method for supplying support means in a coal seam which is to be mined by underground coal gasification.
A further object is to provide a seam equipped with such support means.
Other objects and advantages of this invention will be apparent to one skilled in the art upon reading this disclosure.